1. Field of the Invention
This invention relates to magnetic recording media, and more particularly, to magnetic recording media having a magnetic layer in the form of a continuous thin film formed by the so-called oblique incidence evaporation process.
2. Description of the Prior Art
Among magnetic recording media for use in video, audio and other applications, active research and development works have been made on magnetic recording media, usually magnetic tapes having a magnetic layer in the form of a continuous thin film because of the compactness of a roll of tape.
The preferred magnetic layers for such continuous film type media are deposited films of Co, Co-Ni, Co-O, Co-Ni-O and similar systems formed by the so-called oblique incidence evaporation process. Magnetic layers are formed on substrates by the oblique incidence evaporation process as a coalescence of columnar crystals which extend at an angle with respect to the normal to the major surface of the substrate and have a longitudinal diameter extending throughout the thickness of the magnetic thin layer. Cobalt and optional metals such as nickel and chromium form columnar structure particles themselves while oxygen, when added, is generally present on the surface of each columnar structure particle essentially in the form of oxides. These magnetic thin layers however undesirably develop a considerable difference in input and output characteristics depending on whether the media are transported forward or backward because of the shape anisotropy in the longitudinal direction of the substrate, that is, the direction of transport of the media.